Butanol is an important industrial chemical with a wide range of applications. It can be used as a motor fuel particularly in combination with gasoline to which it can be added in all proportions. Isobutanol can also be used as a precursor to Methyl Tertiary Butyl Ether (MTBE). Currently the world production of n-Butanol is 3.5 million tons/yr. (7.7 billion lb/yr). Furthermore, conversion of alcohols to long-chain linear hydrocarbons that would be suitable for jet fuel use are being developed and demonstrated, which could further increase the demand for n-butanol (The Naval Air Warfare Center-Weapons Division, (2012) Cobalt and Abermarle). Fermentation of carbohydrates to acetone, butanol and ethanol (ABE) is well known and was commercially practiced worldwide from around 1915 to 1955 (Beesch, S. C. (1953). A Microbiological Process Report—Applied Microbiology, 1, 85-95). With the advent of petrochemical processes and low-cost petrochemical feedstocks the carbohydrate-based processes became unattractive and were discontinued.
Attempts have been made to improve the alcohol yield of bacteria that ferment a variety of sugars to acetate and butyrate. The art has sought to employ recombinant techniques to transform bacterium such as C. acetobutylicum (Green et al., 1996 Genetic manipulation of acid formation pathways Microbiology, 142, 2079-2086) and C. tyrobutyricum (X. Liu et al., 2006 Construction and Characterization of an ack Deleted Mutant of Clostridium tyrobutyricum, Biotechnology Progress, 22, 1265-1275). However, such techniques have only resulted in transformation occurring at low frequencies.
Anaerobic acetogenic microorganisms offer a viable route to convert waste gases, such as syngas, to useful products, such as ethanol, via a fermentation process. Such bacteria catalyze the conversion of H2 and CO2 and/or CO to acids and/or alcohols with higher specificity, higher yields and lower energy costs than can be attained by traditional production processes. While many of the anaerobic microorganisms utilized in the fermentation of ethanol also produce butanol as a secondary product, to date, no single anaerobic microorganism has been described that can utilize the syngas fermentation process to produce high yields of butanol.
Thus, there remains a need in the art to produce a biocatalyst bacterium or co-culture of bacteria that produces useful commercial products such as C2-C6 alcohols (including ethanol, propanol, butanol, pentanol and hexanol and any of their isomers).